[This translation,
which has been prepared by Ian Johnston of Malaspina University-College, Nanaimo, BC, Canada, (now
Vancouver Island University) is in the public domain, and may be used by
anyone, in whole or in part, without permission and without charge, provided
the source is acknowledged, released September 1999]

Considerations of the Natural History of Animals, Their Characteristics,
Their Interrelationships, Their Organic Structure, Their Distribution, Their
Classification and Their Species

Chapter Seven

Concerning the Influence of Circumstances on the Actions and Habits of
Animals, and the Influence of the Actions and Habits of these Living Bodies As Causes Which Modify Their Organic Structure and Their
Parts

What
we are now concerned with is not a rational speculation but the examination of
a reliable fact, a more universal one than people think and something to which
we have neglected to pay the attention it deserves. Undoubtedly this is the
case because on most occasions it is very difficult to recognize. This fact
consists of the influence which circumstances exert on the different living
things subject to them.

In
truth, for quite a long time now we have noticed the influence of the different
states of our organic structure on our characteristics, inclinations, actions,
and even our ideas. But it seems to me that no one has get
made known the influence of our actions and habits on our own organic
structure. Now, as these actions and habits are entirely dependent on the
circumstances in which we usually find ourselves, I am going to try to show how
great the influence is which these circumstances exert on the general form, the
condition of the parts, and even on the organic structure of living things.
Thus, this chapter is going to explore this very well established fact.

If we
had not had numerous occasions to recognize quite clearly the effects of this
influence on certain living bodies which we have transported into entirely new
environments, very different from the ones where they used to live, and if we
had not seen these effects and the changes resulting from them come to light in
some way under our very eyes, the important fact under discussion would have
always remained unknown to us.

The
influence of circumstances is truly working always and everywhere on living
bodies. But what makes this influence difficult for us to perceive is that its
effects become perceptible or recognizable (especially in animals) only after a
long passage of time.

Before
laying out and examining the proofs for this
noteworthy fact (something extremely important for Zoological Philosophy),
let us summarize the thread of the ideas with which we started our analysis.

In the
preceding paragraphs, we have seen that it is now an incontestable fact that,
when we consider the animal scale in a sense opposite to the natural direction,
we find that in the groups which form this scale there exists a sustained but
irregular degradation in the organic structure of animals making up the groups,
an increasing simplicity in the organization of living bodies and finally a
corresponding diminution in the number of faculties in these beings.

This
well known fact can provide us the greatest insights into the very order which
nature followed in the production of all animals which she has brought into
existence. But it does not show us why animals’ organic structure, with its
increasing complexity from the most imperfect right to the most improved, only
displays an irregular gradation in which the range manifests a number of
anomalies or gaps which have no apparent order amid their variety.

Now,
in seeking out the reason for this peculiar irregularity in the growing
complexity of animals’ organic structure, if we consider the results of the
influences which the infinitely various circumstances in all the regions of the
earth exert on the general shape, parts, and even the organic structure of
these animals, then everything will be clearly explained.

In
fact, it will be quite clear that the condition in which we see every animal
is, on the one hand, the product of the increasing complexity in organic
structure which tends to create a regular gradation and, on the other hand, the
product of influences of a multitude of very different circumstances which
continuously tend to work against the regularity in the gradations of the
growing complexity in organization.

Here
it becomes necessary that I explain what I mean by the following expression: Circumstances
have an influence on the form and the organic structure of animals. What
this means is that by undergoing significant change, the circumstances
proportionally alter, over time, both the form and the organic structure itself

True,
if someone takes these expressions literally, he would say I was making a
mistake. For no matter what the circumstances can be, they do
not work to bring about directly any modification whatsoever in the shape and
organic structure in animals.

But
significant changes in the circumstances lead, for animals, to great changes in
their needs. Such changes in the needs necessarily lead to changes in their actions.
Now, if the new needs become constant or last a long time, the animals then
acquire new habits which are just as long lasting as the needs which brought
them about. That is what is easy to demonstrate and, indeed, requires no
detailed explanation to be understood.

Thus,
it is clear that a significant change in circumstances, once it becomes
constant for a race of animals, leads these animals to new habits.

Now,
if new circumstances have become permanent for a race of animals and have given
these animals new habits, that is, have driven them to new actions which have
become customary, that will result in the preferential use of one part over
another and, in some cases, in the total disuse of some part which has become
useless.

None
of this should be considered a hypothetical or odd opinion. It is, by contrast,
a truth which requires, to make it perfectly clear,
nothing but attentive observation of facts.

We
will see shortly through references to known facts which attest to these
matters, on the one hand, that once new needs make some part essential, they
effectively, by a sequence of efforts, give rise to that part; later its
sustained use gradually strengthens and develops it, and finally finishes up by
increasing its size considerably. On the other hand, we shall see that in some
cases, the new circumstances and needs made some part totally useless. The
total lack of use of this part brought it about that it gradually ceased
undergoing the development experienced by the other parts. Thus, it grew smaller
and weaker gradually, and finally, when this lack of use had been complete for
a long time, the part in question ended up disappearing. All
that is reliable fact. I propose to give the most convincing proofs of
this point.

In the
plants where there are no actions and consequently, strictly speaking, no
habits, significant changes in circumstances nonetheless lead to significant
differences in the development of their parts. As a result, these different
circumstances give rise to and develop certain parts, while they weaken several
other parts and lead to their disappearance. But here everything exerts its
effect through changes undergone in what the plant uses for nourishment, in
what it absorbs and breathes, in the quality of heat, light, air, and humidity
which the plant customarily then receives, and, finally, through the
superiority which some of these various vital movements can gain over others.

Among
individuals of the same species, if some are continually well nourished in
circumstances favourable to their total development, while others find
themselves in opposite circumstances, then there is produced a difference
between the conditions of these individuals which gradually becomes very
noticeable. How many examples I could cite concerning animals and plants which
confirm the basis for this idea! Now, if circumstances remain the same, making
the condition of the poorly nourished individuals habitual and constant, with
suffering and malnourishment, their interior organic structure is finally changed.
Reproduction among the individuals in question preserves the acquired
modifications and ends up by giving rise to a race very different from the one
made up of individuals who find themselves constantly in circumstances
favourable to their development.

A very
dry spring causes prairie grasses to grow very little, to remain thin and
scrawny, to flower and bear fruit, although they have grown very little.

A
spring mixed with hot days and rainy days brings about in these same grasses a
generous growth, and the harvest of hay is then excellent.

But if
with these plants some causes perpetuate unfavourable circumstances, they will
vary proportionally, at first in their bearing or their general condition, and
later in several specific characteristics.

For
example, if a grain of some prairie grass or other is carried into a high
place, onto a dry, arid, and rocky patch of land very exposed to the wind and
can germinate there, the plant which can live in this place will always find
itself malnourished, and if the individuals which it produces continue to exist
in these poor circumstances, there will result a race truly different from the
one which lives in the prairie (which is, however, the origin of the second
race). The individuals of this new race will be small, scrawny in their parts,
and some of their organs, having undergone more development than others, will
then manifest strange proportions.

Those
who have observed a great deal and consulted large collections have been
convinced that as the conditions in the environment, exposure, climate,
nourishment, way of life, and so on undergo changes, the characteristics of
height, shape, proportions among the parts, colour, consistency, agility, and
industry (for the animals) correspondingly change.

What
nature does with a great deal of time, we do every day, when on our own we
suddenly change the conditions in which a living plant and all the individuals
of its species are found.

All
botanists know that the plants which they take from the place where they were
born to the gardens where they are cultivated undergo there gradual changes
which end up making them unrecognizable. Many naturally very hairy plants in
this way become smooth, or almost so; a number of those which were low and
trailing straighten up their stem; others lose their thorns or protrusions;
still others in our climate change from the woody and perennial stem conditions
which they had in the hot climates where they used to be, to a herbaceous
state, and among them several are nothing more than annuals. Finally, in our
gardens the dimensions of these plants’ parts themselves undergo very
significant changes. The effects of these changed circumstances are so well
recognized that botanists do not like to describe their garden plants until
they are no longer recent cultivations.

Is not
cultivated wheat (triticumsativum) a plant brought by man to the condition in
which we see it today? Can anyone tell me in what country a similar plant lives
naturally, that is, without being the result of its cultivation in some place near by?

Where
do we find in nature our cabbage, lettuce, and so on, in the state where we
produce them in our vegetable gardens? Is the case not the same with respect to
the number of animals which domestication has changed or considerably modified?

How
many different races of chickens and domestic pigeons we have acquired by
raising them in different circumstances and different countries! How futile it
is now to seek to find such animals in nature!

Those
which are the least changed (undoubtedly because their domestication is more
recent and because they do not live in a climate foreign to them) in some of
their parts display differences no less significant through the habits which we
have made them acquire. Thus our domestic ducks and geese find their type again
in wild ducks and geese, but ours have lost the ability to rise up into the
high regions of the sky and to fly across large territories. Finally a real
change has occurred in their parts in comparison with the parts of the animals
of the race from which they originated.

Who is
not familiar with the fact that when some bird from our climate raised in a
cage and living there five or six consecutive years is after that returned to
nature, that is, given back its liberty, it is then no longer in a condition to
fly like those similar to it which have always been at liberty? The slight
change of circumstances working on this individual has, in truth, only
diminished its capacity for flying and, undoubtedly, has not brought about any
alteration in the shape of its parts. But if many successive generations of
individuals of the same race were held in captivity over a long period of time,
there is no doubt that even the shape of the parts of these individuals would
have gradually undergone noticeable changes. This would be all the more
reasonable if, in place of keeping them in a simple captivity constantly
maintained, this circumstance had been simultaneously accompanied by a change
into a very different climate and if these individuals had grown accustomed, by
degrees, to other forms of nourishment and to other actions for obtaining it.
It is certain that these combined circumstances, once they become constant,
would then create imperceptibly a new and totally special race.

Where
do we see now in nature the many races of dogs which, as a result of the
domesticity to which we have reduced these animals, we have brought into
existence in the form they are today? Where do we find these mastiffs,
greyhounds, water spaniels, spaniels, lap dogs, and so on and so on, races
which display among themselves greater differences than those which we
acknowledge as specific differences among animals of the same genus living
freely in nature?

Undoubtedly,
some first unique race, at the time very close to the wolf (if that is not in
itself the true type), was domesticated by man at some epoch or other. This race, which did not then manifest any differences among
its individuals, was gradually dispersed with human beings into different
countries and climates. After some length of time, these same individuals
experienced the influences of their surroundings and of their various habits
which they had been made to acquire in each territory, underwent some
remarkable changes, and formed different special races. Now, human beings, who,
for trade or for some other sort of interest, move over very considerable
distances, carried different races of dogs formed in countries far away into
densely inhabited places, like great capital cities. At that time the crossbreeding
of these races through reproduction thus gave rise successively to all those
which we know about nowadays.

The
following fact proves (with respect to plants) how much a change in some
important circumstance has an influence on changing the parts of living
organisms.

Whenever
the plant ranunculus aquatis is immersed in
water, its leaves are all markedly serrated and finely divided. But when the
stem of this plant reaches the surface of the water, the leaves which develop
in the air are enlarged, round, and simply lobed. If some feet of this plant
succeed in pushing into a soil which is only humid, without being underwater,
their stems then are short and none of their leaves is divided up into tiny
sections.This example gives rise
to the plant ranunculus hedereaceus, which
botanists, when they encounter it, consider a species.

There
is no doubt that, so far as animals are concerned, important changes in the
circumstances where they usually live produce similar changes in their parts.
But here the changes are much slower manifesting themselves than in the plants.
Consequently, they are less perceptible to us and their cause less
recognizable.

As for
the circumstances which have the most power to change the organs in living
bodies, the most influential is undoubtedly the diversity in the locations
where the animals live. But, in addition, there are many others which later
have a considerable influence in producing the effects we are discussing.

We
know that different places have a different nature and quality, on account of
their positions, compositions, and climates. That is easy to notice as we go
through different places differentiated by specific qualities. Here is one
cause of variation in the animals and plants which live in these different
places. But what we do not understand sufficient well and what people even
generally refuse to believe is that each place itself changes, over time, in
exposure, climate, nature, and quality, although so slowly in comparison with
our extents of time that we attribute to that place a perfect stability.

Now,
in both cases, these altered locations change correspondingly the circumstances
relevant to living things who live there. And these
circumstances then produce other influences on these living things themselves.

From
that we perceive that if there are extremes in such changes, there are also
slight modifications, that is to say, intermediate degrees which fill up the
gap between the extremes. Consequently, there are also modulations in the
differences which distinguish what we call species.

Thus,
it is evident that all the surface of the earth displays in the nature and the
situation of the materials which make up its different points a diversity of circumstances
which throughout is allied to the diversity in the forms and the parts of
animals, independent of the special diversity which results necessarily from
the progress in the complexity of organic structure in each animal.

Everywhere
where animals can live, the circumstances which create there an order of things
remain the same for a long time and do not really change except with such an
excessive slowness that man is not capable of perceiving it directly. He is
obliged to consult the monuments to recognize that in each of these places the
order in things which he finds there has not always been the same and to sense
that it will change once again.

The
races of animals living in each of these places must thus preserve their habits
for quite a long time; hence the apparent permanence to us of what we call
species, a permanence which has given rise in us to the idea that these races
are as old as nature.

But in
the different habitable locations on the surface of the earth, the nature and
situation of territories and climates there constitute for animals, as for
plants, circumstances different to all sorts of degrees. The animals inhabiting
these different places must therefore be different from each other not only
because of the state of complexity in the organic structure of each race but
also because of the habits which the individuals of each race have been forced
to acquire there. Moreover, as the naturalist traversing parts of the earth’s
surface sees conditions change in a slightly perceptible way, he always then
sees the characteristics of species changing proportionately.

Now,
the true order of things relevant to consider in all this consists in
recognizing the following:

1. All
slightly remarkable changes later maintained in circumstances where each race
of animals is located works to create in that race a real change in its needs.

2. All
changes in animals’ needs require of them alternative actions to satisfy the
new needs and, consequently, alternative habits.

3.
Since the satisfaction of every new need demands new actions, it requires from
the animal experiencing that need either the more frequent use of some of its
parts which previously it used less often (something which develops and makes
that part grow), or the use of new parts which the needs imperceptibly bring
forth in the animal by the efforts of its interior feeling. This I will
establish very soon by known facts.

Thus,
to reach an understanding of the true causes of so many diverse forms and so
many different habits, examples of which the known animals manifest to us, we
must take into account the fact that the infinitely diversified and slowly
changing conditions in which the animals of each race are successively located
have led, in each of them, to new needs and necessarily to changes in their
habits. Now, once this truth, which one cannot contest, is recognized, it will
be easy to see how animals have been able to satisfy the new needs and to
acquire new habits, if we give some attention to the two following laws of
nature, which observation has always confirmed.

First Law

In every animal which has not exceeded the
limit of its development, the more frequent and sustained use of any organ
gradually strengthens this organ, develops it, makes it larger, and gives it a
power proportional to the duration of this use; whereas, the constant lack of
use of such an organ imperceptibly weakens it, makes it deteriorate,
progressively diminishes it faculties, and ends by making it disappear.

Second Law

Everything which nature has made individuals
acquire or lose through the influence of conditions to which their race has
been exposed for a long time and, consequently, through the influence of the
predominant use of some organ or by the influence of the constant disuse of
this organ, nature preserves by reproduction in the new individuals arising
from them, provided that the acquired changes are common to the two sexes or to
those who have produced these new individuals.

These
are the two constant truths which cannot be overlooked except by those who have
never observed nor followed nature in her work or by those who have let
themselves be led into the error which I am going to contest.

Once
naturalists noticed that the forms of animals’ parts are always linked to the
use of these parts, they thought that the forms and the condition of the parts
had led to the usage. Now, there is the mistake. For it is easy to demonstrate
through observation that, by contrast, it is the needs and the use of the parts
which have developed them, factors which even produced the parts at a time when
they did not exist and which, consequently, gave rise to the condition in which
we see them in each animal.

In
order for that not to be the case, it would have been necessary for nature to create
for the animal parts as many forms as required by the diversity of
circumstances in which they have to live and that these forms, as well as the
circumstances, never change.

That
is certainly not the natural order which exists. If it had ever really been
like that, we would not have race horses in the form of those in England; we
would not have our large draught horses, so heavy and different from these race
horses, for nature on her own did not produce anything like them. For the same
reason we would not have basset hounds with crooked limbs, such swift-running
greyhounds, water spaniels, and so on. We would not have tailless hens, fantail
pigeons, and so on. Finally, we would be able to cultivate wild plants as much
as we liked in the rich fertile soil of our gardens, without fear of seeing
them change through long cultivation.

In
this matter, for a long time we have had a feeling for what is really the case,
because we developed the following sentence, which has become proverbial and
universally known: habits form a second nature.

To be
sure, if habits and the nature of every animal were incapable of ever changing,
the proverb would be false, would not have arisen, and would not have been able
to be preserved in the event someone had proposed it.

If one
considers seriously everything which I have just revealed, one will sense that
I grounded my views rationally when in my work entitled Research Into Living Bodies (p. 50), I laid down the following
proposition:

“It is
not the organs, that is, the nature and the form of the animal’s body parts,
which have given rise to its habits and special faculties, but, by contrast,
its habits, manner of life, and circumstances of the individuals from which the
animal comes to possess, over time, the form of its body, the number and
condition of its organs, and finally the faculties which it enjoys.”

Let
people consider well this proposition and bring to it all the observations
which nature and the state of things enable us to make all the time. Then its
importance and reliability will become for us the most significant evidence.

Favourable
times and circumstances are, as I have already said, the two main means
employed by nature to bring into existence all her productions. We know that
time has no limits for her and that, as a result, she always has time to spare.

As to
the circumstances which she needed and which she still uses every day to vary
everything which she continues to produce, we can say that circumstances are,
in some way, for her inexhaustible.

The
main circumstances arise from the influence of climates, various temperatures
in the atmosphere and all the environmental surroundings, the variety of places
and their exposure, habits, the most ordinary movements, the most frequent
actions, finally the means of self-preservation, reproduction, and so on.

Now,
as a result of these various influences, the faculties expand and grow stronger
through use. With new habits preserved over a long time they diversify. Imperceptibly
the arrangement, consistency, in a word, the nature and the condition of the
parts, as well as the organs, undergo the consequences of all these influences,
preserving and propagating themselves in reproduction.

These
truths, which are only the consequences of the two natural laws set forth
above, are, in every case, amply confirmed by the facts. They indicate clearly
the march of nature in the variety of her productions.

But
instead of contenting ourselves with generalities which we could consider
hypothetical, let us examine the facts directly. Let us consider in animals
what is produced by the use or lack of use of their organs on these very
organs, according to the habits which each race has been compelled to acquire.

Now, I
am going to prove that the constant lack of exercise with respect to an organ
at first reduces its faculties, then gradually shrinks it, and ends up by
making it disappear or even destroying it, if this lack of use continues for a
long time in a sequence of successive generations of animals of the same race.

Then I
will reveal how, by contrast, the habit of exercising an organ, in every animal
which has not reached the limit in the diminution of its faculties, not only
improves this organ’s faculties and makes it grow, but also makes it develop
and acquire dimensions which imperceptibly change it, so that in time it makes
it quite different from the same organ examined in another animal which
exercises it much less.

The
lack of use of an organ, once it has become constant because of the habits
which one has taken up, gradually diminishes that organ and ends up by making
it disappear and even destroying it.

Since
such a claim cannot be accepted without demonstrations (and not by a simple
declaration), let us try to set out evidence by citing the major known facts
which constitute the basis for it.

The
vertebrate animals, in all of whom the design of the organic structure is
almost the same, although they manifest much diversity in their parts, have
their jaws equipped with teeth. However, in those among them in which
circumstances have developed the habit of swallowing the objects on which they
feed without previously chewing them at all, we find that their teeth have not
undergone any development. Thus, these teeth either have remained hidden
between the bony layers of the jaws, without being capable of appearing on the
outside, or have even been destroyed right down to their basic elements.

In the
whale, which we thought entirely without teeth, M. Geoffroy
has found them hidden in the jaws of the fetus of the animal. This professor
has also located in birds the groove where the teeth must have been placed. But
we do not see them there any more.

Even
in the class of mammals, which includes the most perfect animals, mainly those
in which the design of the organic structure of vertebrates has been effected
most completely, not only does the whale have no more teeth to use, but we also
find there in the same class the ant eater (Myrmecophaga)
in which the habit of not chewing has been introduced and preserved for a long
time in the species.

Having
eyes in the head is characteristic of a large number of various animals and is
an essential part of the design in the organic structure of vertebrates.

Nevertheless,
the mole which, through its habits, makes very little use of sight,
has only very small eyes, hardly apparent, because the animal makes use of this
organ very rarely.

The aspalax of Olivier (Voyage in Egypt and in Persia,
II, pl. 28, f. 2), which lives underground, like the mole, and which probably
exposes itself to the light of day even less than that animal, has completely
lost the use of sight. Moreover, it manifests no more than vestiges of the
organ which is the seat of sight. In addition, these vestiges are completely
hidden under the skin and under some other parts which cover them over and do
not provide any more the least access to light.

The Proteus,
an aquatic reptile related (by its affinities) to the salamanders and living in
deep and dark cavities under the water, like the aspalax,
has only vestiges of the organs of sight, vestiges which are covered and hidden
in the same manner.

Here
is a decisive consideration concerning the question which I am at present
raising.

Light
does not penetrate everywhere. Consequently, animals who habitually live in the
the places where there is no light lack the
opportunity to exercise the organ of sight, if nature has furnished them with
one. Now, the animals which are part of a structural design in which the
eyes are necessarily a part must have had them in their origins. However,
since we find among these animals ones which are without the use of this organ
and which have only hidden and covered vestiges of it, it becomes evident that
the diminution and even the disappearance of the organ in question are the
results, for this organ, of a constant lack of exercise.

What
proves the point is the fact that the organ of the ear is never like
this. We always find it in those animals in which the nature of their
organic structure requires that the ear be present. Here is the reason.

The
material of sound (1), which is set
in motion by the shock or the vibration of bodies, transfers to the organ of
hearing the impression which it has received, penetrates everywhere, and moves
through every medium, even the masses of the densest bodies. The result
is that every animal which is part of an organic structural design in which the
ear is an essential part always has the opportunity to exercise this organ in
whatever place it dwells. Thus, among the vertebrate animals we do not
witness any which lack the organ of the ear, and after that point, when this
same organ is lacking, we do not find it again later in any of the animals of
the later classes.

Such
is not the case with the organ of sight, for we see this organ disappear,
reappear, and disappear once more, as a result of the possibility or the
impossibility of the animal’s making use of it.

In the
acephalid mollusks, the great development of the
mantle has made their eyes and even their head entirely useless. Although
these organs are part of a structural plan which should include them, they have
therefore had to disappear and die out through a constant lack of use.

Finally,
part of the organic structural design of reptiles, as in other vertebrate
animals, includes having four limbs dependent on their skeleton.
Consequently, snakes should have four of them, especially since they do not
make up the last order of reptiles and since they are more distant from the
fish than are the batrachians (frogs, salamanders, and so on).

However,
snakes took up the habit of crawling on the ground and hiding in the
grass. Thus, their body, as a result of constant and repeated efforts to
extend itself, so as to pass into narrow spaces,
acquired a considerable length, totally disproportionate to its size.
Now, limbs would have been really useless to these animals and consequently
remained unused (for extended limbs would have been an impediment to their need
to crawl, and very short limbs, necessarily four in number, would have been
incapable of moving their bodies). Thus the lack of use of these parts,
remaining constant for the races of this animal, made these very parts
disappear entirely, although the limbs were actually in the design of the
organic structure of animals of their class.

Many
insects which, according to the natural characteristics of their order and even
their genus, should have wings, lack them more less completely, because they do
not use them. A number of coleoptera, orthopetera, hymenoptera, and hemiptera,
and so on give us examples of this fact. The habits of these animals
never put them in situations where they used their wings.

But it
is not sufficient to provide an explanation for the cause which has led to the
state of the organs of different animals, a condition which we observe is
always the same in those of the same species. In addition, it is
necessary to make known the alterations brought about in the organs of a single
individual during its lifetime,.solely
as the product of a great mutation in the habits unique to the individuals of
its species. The following extremely remarkable fact will complete the
proof of the influence of habits on the condition of the organs and establish
how much sustained changes in the habits of an individual lead to changes in
the condition of the organs which are brought into action during the exercise
of these habits.

Mr. Tenon, member of the Institute, has made known to the Class
of Sciences, that he examined the intestinal canal of several men who had been
passionate drinkers for a large part of their lives. He constantly found
the organ shortened by an extraordinary amount in comparison with the same
organ in all those who had not picked up the same habit.

We
know that great drinkers, or those who have been addicted to drinking, eat very
little solid food, that they eat almost nothing, and that the drink which they
consume in abundance and frequently is sufficient to nourish them.

Now,
since the alimentary fluids, especially spirit drinks, do not stay for long
either in the stomach or in the intestine, among drinkers the stomach and the
rest of the intestinal canal lose the habit of being distended, just as the
stomachs of sedentary persons constantly busy with intellectual work who are
accustomed to eating only a little gradually over time contract, and their
intestines grow shorter.

This
matter is not at all a question of a shrinking and a contraction brought about
by a gathering in of the parts which would allow for an ordinary extension if
these internal organs were filled, rather than undergoing a sustained
emptiness. It is rather a question of a real and considerable shrinkage
and contraction such that these organs would break rather than yield suddenly to
causes which demand an ordinary extension.

Compare,
at entirely similar ages, a man who, in order to free himself for studies and
habitual intellectual work, has acquired the habit of eating very little with
another who habitually takes plenty of exercise, frequently goes out of his
house, and eats well. The stomach of the first will have very little
capacity and will be filled by a very small quantity of nourishment, while the
stomach of the second will have preserved and even increased its capacity.

There
we have an organ strongly modified in its dimensions and capacity by the single
cause of a change in habits over the lifetime of an individual.

The
frequent use of an organ, once it becomes constant and habitually, increases
the capacities of this organ, develops it, and makes it acquire dimensions and
an active power which the organ does not possess in the animals which exercise
it less.

It has
just been shown that the lack of use of an organ which ought to exist modifies
it, diminishes it, and ends up destroying it.

Now I
am going to establish that the continuous use of an organ, along with the
efforts made to derive from it a substantial benefit in circumstances which
demand it, fortifies the organ, extends and enlarges it, or makes new organs
from it which can carry out functions which have become essential.

The
bird drawn to water by the need to to find there prey which sustains its life extends the digits on
its feet with which it wishes to strike the
water and move on the surface. The skin which unites these digits at
their base, because of these constantly repeated separations of the digits,
acquires the habit of stretching itself. Thus, over time, the large
membranes which link the digits of ducks, geese, and so on are formed just as
we see them. The same efforts made for swimming, that is, to push the
water in order to advance and move in this liquid have in the same manner
extended the membranes between the digits of frogs, sea-tortoises, otter,
beaver, and so on.

By contrast,
the bird whose way of living accustoms it to perching in trees and which
descends from individuals which have all acquired this
habit, necessarily has longer digits on its feet shaped in a different way from
those of the aquatic animals which I have just cited. Its claws, over
time, grow longer, sharper, and hook-like to grasp the branches on which the
animal rests so often.

In the
same way, we see that the shore bird which has no inclination to swim but which
nevertheless needs to approach the water’s edge to find its prey constantly
runs the risk of sinking down in the mud. Now, this
bird, wishing to act in such a way that its body does not sink in liquid, makes
every effort to extend and lengthen its feet. From that it follows
that the long habit which this bird and all those of its race acquire of
extending and lengthening their feet brings it about that the individuals of
this race find themselves elevated as if on stilts, having gradually developed
long bare legs, that is, legs without feathers up to the thighs and often
further than that. Système des Animaux sans vertèbres, p.
14.

We
also know that the same bird, wishing to fish without getting its body wet, is
required to make continual efforts to lengthen its neck. Now, the
consequences of these habitual efforts in this individual and in those of its
race must have, over time, lengthened their necks remarkably, a point which is,
in fact, confirmed by the long neck of all shore birds.

If
some swimming birds, like the swan and the goose, in which the legs are short,
have nonetheless a very long neck, the reason is that these birds, while moving
along on the water, are accustomed to plunge their heads down into it as deeply
as they can to take from there the aquatic larvae and different animalcules on
which they feed. They make no effort to lengthen their limbs.

If an
animal, in order to satisfy its needs, makes repeated efforts to lengthen its
tongue, that organ will acquire a considerable length (anteater, green
woodpecker). If the animal needs to seize something with this same organ,
then its tongue will divide and become forked. The tongue of the humming
birds, whoseize things with
their tongue, and that of lizards and snakes, who use their tongues to feel and
recognize the bodies in front of them prove what I am proposing.

Needs,
always induced by circumstances, and the later efforts maintained to satisfy
those needs are not limited in the results of their modifications, that is, in
increasing or diminishing the extent and the capacities of organs. But
they also succeed in removing these same organs, when certain of these needs
are not essential.

The
fish which customarily swim in large bodies of water have a need to see
laterally. They, in fact, have their eyes placed on the sides of their
heads. Their bodies, more or less flattened, depending on the species,
have their edges perpendicular to the plane of the water, and their eyes are
placed in such away that there is one eye on each
flat side. But those fish whose habits require them constantly to come
close to the shore, particularly to shores slightly inclined or with a gentle
slope, have been forced to swim on their flattened side, in order to be able to
approach more closely the edges of the water. In this situation, receiving
more light from above than below and having a special need to be always
attentive to what is found above them, their need has induced one of their eyes
to undergo a sort of displacement and to occupy the very remarkable position
that we know about in soles, turbots, dabs, and so on (the Pleuronectesand Achirus). The location of these
eyes is no longer symmetrical, because it results from an incomplete
mutation. Now, this mutation is completely realized in the skates, where
the transverse flattening of the body is totally horizontal, as well as the
head. Thus, the eyes of rays, both placed on the upper surface, have
become symmetrical again.

The
snakes, which crawl on the surface of the earth, need mainly to see elevated
objects which are above them. This need must have influenced the
placement of the organ of sight in these animals. In fact, they have
their eyes situated in the lateral and upper part of the head, in such a way
that they can easily perceive what is above them or beside them. But they
hardly see at all what is in front of them a very short distance away.
However, forced to make up for this defect of vision for understanding the
bodies which are in front of their heads and which might injure them if they
moved forward, they were not able to perceive these bodies except with their
tongue, which they were obligated to extend with all their force. This
habit not only helped to make this tongue thin, very long, and contractile, but
also it has also forced the tongue to divide itself in the majority of species
in order to feel several objects at once. It even permitted them to form
an opening on the edge of their muzzle, so that they could move the tongue
through it without separating their jaws.

Nothing
is more noteworthy than what is produced by the habits of the herbivorous
mammals.

The
quadrupeds in which circumstances and the needs created by these over a long
period of time have developed (in it as well as in the individuals of the race)
the custom of grazing on grass, moves only on the ground, and finds itself
obliged to remain their on its four feet for most of
its life, not generally carrying out much movement (or only moderate
movement). The large amount of time this sort of animal is required to
use each day to fill itself up with a single form of nourishment to which it is
accustomed brings it about that it exercises itself very little by moving
around and that it uses its limbs only to hold it up on the earth, to move or
to run, and it never makes use of its limbs to cling to and climb up trees.

From
this habit of consuming, every day, huge volumes of material for nourishment,
which distends the organs taking it in, and from the habit of only carrying out
moderate movements the result is that the bodies of these animals have grown
considerably thicker, have become heavy and huge, and have acquired a really
large volume, as we see in elephants, rhinoceroses, oxen, buffaloes, horses,
and so on.

The
habit of staying upright on four feet for the greater part of the day in order
to graze has given rise to a thick horn which envelops the digits of their
feet. And since these digits have rested without being exercised by any
movement and since they have not served any other purpose than to hold the
animals up (just like the rest of the foot) most
of these digits have shrunk, dwindled, and have finally disappeared.
Thus, in the pachyderms, some have on their feet five digits enveloped in horn
and, consequently, their hoof is divided into five parts; others have only four
and still others have only three. But in the ruminants, which appear to
be the oldest of the mammals limited to sustaining themselves only on land,
there are no longer more than two digits on the feet, and in the solipeds there is only one (horses, donkeys).

However,
among the herbivorous animals, and particularly among the ruminants, it
happens that there are some which, due to circumstances in the desert countries
which they inhabit, are ceaselessly in danger of being the prey of carnivorous
animals and which can find safely only in sudden flight. Necessity has
thus forced them to practice rapid running. From the
habit which they have acquired from that, their bodies have become more svelte
and their limbs much more slender. We see examples of them in
antelopes, gazelles, and so on

In our
climate, other dangers continually expose the red deer, roe deer, and fallow
deer to the mortal peril of hunting by human beings and reduce the animals to
the same need, force upon them similar habits, and have given rise to the same
productions with respect to them.

Ruminant
animals can make use of their feet only to hold themselves up. Since they
have little power in their jaws, which are exercised only by cutting and
browsing on grass, they cannot fight each other except with blows of the head,
aiming the crown of their heads against each other.

In
their fits of anger (which are frequent, above all among the males), their
inner feeling, in these efforts, very strongly direct the fluids towards this
part of their heads and there create a secretion of horny material in some and
in others a bony material mixed with horny material. This gives rise to
solid protuberances. Hence, the origin of horns and
antlers, with which the heads of the majority of these animals are armed.

In
this matter of habits, it is remarkable to observe the result in the peculiar
form and height of the giraffe (camelo-pardalis).
We know that this animal, the largest of the mammals, lives in the interior of
Africa and dwells in those places where the earth, almost always arid and
without grass, requires the animal to browse on the foliage of trees and
constantly to try hard to reach that foliage. As a result of this habit,
maintained for a long time in all the individuals of its race, the animal’s
front limbs have become longer than those at the back, and its neck has grown
longer to such an extent that the giraffe, without rearing up on its hind legs,
lifts its head and reaches up to six metres in height (close to twenty feet).

Among
the birds, the ostriches, lacking the capacity to fly and elevated on very high
limbs, probably owe their remarkable form to analogous circumstances.

The
result of habits is just as noteworthy in the carnivorous mammals as it is in
the herbivores. But it manifests effects of a different sort.

In
fact, among these mammals those who are accustomed, along with their
race, to climb, to scratch away in order to dig a hole in the ground, or
to rip apart other animals which they attack and kill for prey have a need to use
the digits on their feet. Now, this custom has favored the separation of
their digits and has formed the claws with which we see them equipped.

But
among the carnivores, there are those which are obliged to run in order to
catch their prey. Now, among these animals those in which need (and
consequently custom) has made it necessary every day for them to rip with their
claws and to push them deep into the body of another animal in order to hang on
to it and finally to make an effort to tear out the part they have seized must
have, through repeated efforts, acquired for these claws a size and curved
shape which would have then made them very
awkward for walking or running on stony ground. In this case, what
happened was that the animal was obliged to make other efforts to push back
these excessively projecting curved claws which got in its way. From this
gradually resulted the formation of these remarkable
sheaths in which cats, tigers, lions, and so on withdraw their claws when they
are of no use.

Thus,
efforts made in any direction whatever, if maintained for a long time or
habitually made by certain parts of a living body to satisfy needs demanded by
nature or circumstances enlarge these parts and make them acquire dimensions
and a shape which they would never have attained if these efforts had not
become the habitual action of the animals which carried them out.
Observations undertaken on all the known animals provide examples of this
everywhere.

Is
it possible that there is a more striking one than the kangaroo? This
animal, which carries its little ones in the pouch which it has under its
abdomen, has acquired the habit of holding itself upright, balanced only on its
back feet and its tail, and it does not move except with the help of a series
of leaps in which it maintains its upright posture so as not to upset its
young. From this come the following:

1. Its
front limbs, of which it makes very little use and on which it leans only in
the moment when it abandons its upright posture, have never undergone a
development proportional to that of the other parts and have remained thin,
very small, and almost without force.

2. The
back limbs, almost constantly in action, whether to hold up all the body or to
carry out its jumps, have, by contrast, undergone a considerable development
and have become very large and very powerful.

3.
Finally, the tail which we see here used a great deal to hold the animal up and
for carrying out its principal movements has acquired at its base an extremely
remarkable thickness and power.

These
well known facts are surely very relevant to show what results from the
habitual use among animals of an organ or any part whatever. And if, when
one observes in an animal, an organ noticeably developed, strong, and powerful,
people maintain that habitual exercise has done nothing to bring that about,
that its sustained lack of use would not take anything away, and that finally
this organ has always been just as it is now ever since the creation of the species
to which this animal belongs, I will enquire why our domestic ducks cannot fly
any more like wild ducks. In a word, I will cite a multitude of examples
directly relevant to us which point to the different results of the exercise or
the lack of exercise of any of our organs, although these differences might not
be maintained in individuals who come later
through reproduction.

I will
make known in the second part that, when will power determines that an animal
carry out some action or other, the organs which must execute this action are
immediately stimulated to it by the inflow of subtle fluids (the nervous
fluids) which become there the determining cause of the movements which the
action in question demands. A multitude of observations confirms this
fact, which people cannot now doubt.

From
this it follows that multiple repetitions of these actions of the organic
structure strengthen, extend, develop, and even create organs essential for
these actions. It is only necessary to observe attentively what happens
everywhere in this matter to become convinced of the basis for this cause of
developments and organic alterations.

Now,
every change acquired in an organ by a habitual use sufficient to have brought
it about then preserves the change by reproduction, if it is common to
individuals which, in the act of reproduction, come together for the
propagation of their race. Finally, this change passes itself on and thus
is transmitted to all the individuals which come after
and which are subject to the same circumstances, without being obliged to
acquire the change in the same way it was actually created.

Moreover,
in the reproductive unions, the blending of individuals who have different
qualities and forms is necessarily opposed to the constant propagation of these
qualities and forms. In man, who is subjected to so many diverse
influential circumstances, that is what prevents the accidental qualities or
defects which he happens to acquire from preserving and propagating themselves
by reproduction. If we have a case where two individuals with remarkable
shapes or any defects always couple together, they will reproduce the same
particular features, and if later generations limit themselves to similar
unions, a particularly distinct race will then be formed from them. But
constant interbreeding among individuals who do not have the same distinctive
features will erase all distinctive particularities acquired by distinctive
circumstances. Hence, we can be assured that if the distance between their
dwelling places did not separate human beings, the reproductive mixing would do
away with the general characteristics which distinguish the different nations.

If I
wished here to review all the classes, all the orders, all the genera, and all
the species of animals which exist, I could show that the structure of
individuals and their parts, their organs, their capacities, and so on and so
on, are everywhere uniquely the result of the circumstances which each race
finds itself subjected to by nature and of the habits which the individuals
making up a race have been obliged to acquire. I could show that these are not
the result of a form existing in primitive times which has forced animals into
those habits which we know about.

We
know that the animal called the ai, or the sloth (bradypustridactylus)
is constantly in a feeble state, so much so that it carries out only very slow
and very limited movements and that it moves on the ground with difficulty. Its
movements are so slow that people allege that it can make only fifty paces in a
single day. We also know that the organic structure of this animal is entirely
linked to its feeble condition or its inability to move and that if it wished
to make movements different from those which we have seen it carry out, it would not be able to.

Hence,
by assuming that this animal had received from nature the organic structure
which we know about, people said that this organization forced upon it the
habits and the sorry condition in which it finds itself.

I am a
long way from believing this. For I am convinced that the
habits which individuals of the sloth family were forced to acquire originally
must necessarily have led to its present condition.

If
continual dangers had in earlier times brought it about that individuals of
this species took refuge in the trees, habitually lived there, and derived
nourishment from their leaves, then it is clear that
they would have had to forgo a multitude of movements which animals living on
the ground are in a position to carry out. All the needs of the ai would thus have been reduced to hanging from branches,
crawling or dragging themselves along there to catch leaves, and finally
remaining in the tree in an inactive state so as to avoid falling down.
Moreover, this style of inactivity would have been constantly fostered by the
hot climate, because among warm-blooded animals heat encourages rest rather
than movement.

Now,
over a long period of time, the individuals of the sloth family would have
continued the habit of remaining in the trees and not moving there other than
slowly and with little variety, in a way which could meet their needs. Their
organic structure gradually would have accorded itself to their new habits.
From that, the following will result:

(1) the arms of these animals, by making constant efforts to
hold readily onto the tree branches, would have grown longer;

(2) the nails on their digits would have acquired considerable
length and a hooked shape, through the sustained efforts of the animal to hold
onto its position;

(3) since their digits would never be exercised with remarkable
movements, they would have lost all their mobility, grown together, and
preserved only the ability to clench or unclench all together;

(4) since their thighs would continually wrap around the trunk
or the large tree branches, they would have acquired a customary space between
them, something which would help to enlarge the pelvis and to push the cotyloid cavities towards the back;

(5) finally, a large number of their bones would have fused
together and several parts of their skeletons would have taken on an
arrangement and a shape corresponding to the animals’ habits, something
different from what they would have to have for other habits.

There
we have what people will never be able to doubt, because, in fact, nature, in a
thousand different cases, always shows us analogous facts, in the power of
circumstances on the habits and of habits on shapes, arrangements, and
proportions of animals.

Since
a greater number of references is quite unnecessary, here we have what the
point of this discussion comes down to.

The
fact is that the various animals all have, in accordance with their genus and
their species, particular customs and always an organic structure which accords
perfectly with these customs.

From a
consideration of this fact, it seems that we are free to admit that either one
or the other of the two following conclusions and that neither of them can be
proven.

Conclusion
Accepted Up Until Today: Nature (or its author), in creating the animals,
anticipated all the possible sorts of circumstances in which they would have to
live and gave to each species a fixed organic structure, as well as a
determined and invariable form for its parts, which forces each species to live
in those places and climates where it is located and to maintain there the
habits which we know it has.

My
Personal Conclusion: Nature, by producing in succession all the animal species
and beginning with the most imperfect or the simplest, gradually made the
organic structure more complicated; as these animals generally spread out into
all the habitable regions of the world, from the influence of the circumstances
which each species encountered, it acquired the habits which we know in it and
the modifications in its parts which observation reveals to us in that species.

The
first of these conclusions is the one which people have drawn up to the present
time, that is to say, that it has been just about universal. It assumes in each
animal a constant organic structure and parts which have never varied and which
will never vary; it further assumes that the circumstances in the places where
each species of animals dwells never varies in these locations; for if they did
vary, the same animals would no longer be alive and the possibility of finding other
similar circumstances and of transporting themselves there would be forbidden
to them.

The
second conclusions is my own. It assumes that
through the influence of circumstances on habits and later the influence of
habits on the condition of the parts and even on the condition of the organic
structure, each animal can undergo in its parts and organic structure
modifications capable of becoming really significant. This has given rise to
the condition in which we find all the animals.

To
establish that this second conclusion is groundless, it is first necessary to
prove that each point on the surface of the earth never varies its nature,
exposure, lofty or low elevation, its climate, and so on and so on, and, beyond
that, to show that no part of animals undergoes, even with the passage of a
great deal of time, any modification occasioned by a change in its
circumstances and by the necessity which forces them to a style of life and
action different from what is habitual to them.

Now,
if a single fact confirms that an animal which has been domesticated for a long
time differs from the wild species from which it originated and if, in such a
domesticated species, we find a great structural differences between
individuals which we have subjected to some habit and those whom we have forced
into different habits, then it will be certain that the first conclusion does
not conform at all to natural laws and that, by contrast, the second is perfectly
in accordance with them.

Thus,
everything comes together to establish my assertion, namely, that is is not the form (wether of the
body or the parts) which gives rise to the habits and the manner of living in
animals, but that, by contrast, it is the habits, the manner of life, and all
the other influential circumstances which have, over time, shaped the form of
the body and the parts of animals. With new shapes, new faculties were
acquired, and gradually nature came to the point of creating the animals such
as we see them now.

Could
there be in natural history a more important conclusion, one to which we ought
to give more attention, than the one with I have just revealed?

Let us
conclude this first part with the principles and the exposition of the natural
order of animals.

Notes to Chapter
Seven

(1)
Physicists think and even state that atmospheric air is the unique medium for
sound, that is to say, that it is the air which, set in motion by the shocks or
the vibrations of bodies, transmits to the organ of the ear the impressions of
the oscillations which it has received.

That
this view is an error is confirmed by a number of known facts which prove that
it is impossible for air to penetrate to all regions where the material
producing sound actually does penetrate.

See my
Memorandum on the substance of sound, printed at the end of my Hydrogeology,
p. 225, in which I have set forth the proofs of this mistake.

Since
the publication of my memorandum (which people have been reluctant to refer to)
great efforts have been made to reconcile the known velocity for the
propagation of sound in air with the sluggishness of the air particles which
makes the propagation of these oscillations too slow to equal this speed.
Now, since the air in its oscillations necessarily undergoes successive
compression and dilation in parts of its mass, people have used the products of
the calories given off in the sudden compression of air and of those absorbed
in the rarefaction of this fluid. Thus, by using the results of these
products and their size, as determined by appropriate hypotheses, geometricians
now provide a rational basis for the speed with which sound propagates itself
in air. But that does not square at all with facts which confirm that
sound propagates itself through bodies which air is
incapable of moving through or of setting any of its parts in motion.

In
fact, the assumption concerning the vibration of the smallest parts of solid
bodies is a very doubtful oscillation which cannot propagate itself except in
homogeneous bodies with the same density and cannot extend from a dense body
into a rarefied body, nor from the latter into another very dense body. This
assumption cannot be reconciled with the well known fact about the propagation
of sound through heterogeneous bodies with different densities and very
different natures. [Back to Text]